Re: [PATCH 03/27] ext4: don't write back data before punch hole in nojournal mode

Jan Kara
2024-12-04T11:27:07Z

On Tue 22-10-24 19:10:34, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@huawei.com>
>
> There is no need to write back all data before punching a hole in
> data=ordered|writeback mode since it will be dropped soon after removing
> space, so just remove the filemap_write_and_wait_range() in these modes.
> However, in data=journal mode, we need to write dirty pages out before
> discarding page cache in case of crash before committing the freeing
> data transaction, which could expose old, stale data.
>
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>

With the ext4_truncate_page_cache_block_range() function I propose, this
will get slightly simpler. But overall the patch looks good.

Honza

> ---
> fs/ext4/inode.c | 26 +++++++++++++++-----------
> 1 file changed, 15 insertions(+), 11 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index f8796f7b0f94..94b923afcd9c 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3965,17 +3965,6 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
>
> trace_ext4_punch_hole(inode, offset, length, 0);
>
> - /*
> - * Write out all dirty pages to avoid race conditions
> - * Then release them.
> - */
> - if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
> - ret = filemap_write_and_wait_range(mapping, offset,
> - offset + length - 1);
> - if (ret)
> - return ret;
> - }
> -
> inode_lock(inode);
>
> /* No need to punch hole beyond i_size */
> @@ -4037,6 +4026,21 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
> ret = ext4_update_disksize_before_punch(inode, offset, length);
> if (ret)
> goto out_dio;
> +
> + /*
> + * For journalled data we need to write (and checkpoint) pages
> + * before discarding page cache to avoid inconsitent data on
> + * disk in case of crash before punching trans is committed.
> + */
> + if (ext4_should_journal_data(inode)) {
> + ret = filemap_write_and_wait_range(mapping,
> + first_block_offset, last_block_offset);
> + if (ret)
> + goto out_dio;
> + }
> +
> + ext4_truncate_folios_range(inode, first_block_offset,
> + last_block_offset + 1);
> truncate_pagecache_range(inode, first_block_offset,
> last_block_offset);
> }
> --
> 2.46.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR